Sugar alcohols such as sorbitol and mannitol have hitherto been known to have crystals or crystalline mixture solids, and a variety of methods for producing them have already been known.
In contrast with mannitol or sorbitol of which cystals have hitherto been known, maltitol tends to form a supersaturated state more readily and thus hardly forms a crystal. The methods for producing a crystal or a crystalline mixture solid of it have been invented only recently, and it was believed impossible to produce a crystal from maltitol prior to this invention as described by JIRO NIKUNI, DENPUN KAGAKU HANDBOOK, lines 14 and 17-18 of p. 461 (published from ASAKURA SHOTEN, Jul. 20, 1977).
The crystals of maltitol or the crystalline mixture solid containing maltitol have been prepared for the first time in 1981, and the methods for producing them are disclosed in TOKKYO-KOKOKU-KOHO (Publication for Opposition of Examined Patent Application) SHOWA 63(1988)-2439.
The crystalline mixture solid containing maltitol holds a place in its commercial market more important than crystals obtained by the fractional crystallization method because of its excellent properties and for economical reasons.
The crystalline mixture solid containing maltitol, however, has many ambiguous points on the physical behaviors for producing its crystalline mixture solid, as it is not long since the discovery of the crystalline mixture solid containing maltitol and it tends to form a supersaturated state very easily. Therefore, the crystalline mixture solid containing maltitol was produced only by a limited method.
The method for producing the crystalline mixture solid containing maltitol disclosed in the aforementioned TOKKYO-KOKOKU-KOHO comprises dissolving maltitol having a purity of 65% or more (unless otherwise described, % means % by weight hereinafter) into water to form an aqueous solution of maltitol having a concentration of about 65-95%, and forming a mascuite by the co-existence of a seed crystal. Such method in itself is provided for any one of the well-known methods of a block grinding method, a fluidized drying method or a spray-drying method.
For example, the spray-drying method is generally a method which comprises spraying a mascuite having a concentration of about 70-85% and a crystallization rate in the range of about 25-60% from a nozzle of a high-pressure pump and maturing the sprayed mascuite under the hot air at a temperature of 60.degree.-100.degree. C. which will not cause the melting of crystalline powder for about 1-20 hours.
The block grinding method is generally a method which comprises standing a mascuite having a water content of about 5-15% and a crystallization rate in the range of 10-60% for 0.5-5 days to crystallize and solidify the whole of the mascuite in the form of a block, which is then ground by a grinding or cutting method and dried.
Among these methods, the block grinding method, in spite of its complicated processes, is used as a major method for producing the crystalline mixture solid containing maltitol for the reasons that each process can be carried out relatively readily and that the scale of the installation and the process costs are cheaper as compared with those of the other two methods.
The crystalline mixture solid containing maltitol obtained by these methods had an apparent specific gravity in the range of about 0.43-0.59 in the form of a powder having a particle size of 20-50 mesh and was lighter than the other sugar alcohols such as sorbitol or the like. Furthermore, the crystalline mixture solid containing maltitol had a high oil absorptivity in the range of 15-22%, and a relatively thin porous crystalline structure was observed with a scanning electron micrograph having a magnification of about 1,000.
The crystalline mixture solid containing maltitol prepared by the aforementioned conventional methods had many problems with its physical properties.
For example, (a) the crystalline mixture solid containing maltitol prepared by the conventional method was bulky in its volume because of its small apparent specific gravity, and a packaging material or a packaging vessel used for the other sugar alcohols and originally having a capacity satisfactory to hold a certain amount of such other sugar alcohols was insufficient to hold the full volume of the same weight of a crystalline mixture solid containing maltitol, so that a packaging material or a packaging vessel for its exclusive use is required and a large space or a conveying apparatus is also required for the storage or conveyance of it;
(b) the powder of it is light in weight and thus the fine powder tends to be scattered, so that its use is limited; and PA1 (c) it has a thin crystal structure, so that a tablet prepared by the direct punching of it tends to have an insufficient hardness.
There also remained many problems in the conventionally described fluidized drying method and the spray-drying method as well as the block grinding method which has been conventionally used.
For example, the fluidized drying method is a method in which the crystal of maltitol or the crystalline mixture solid containing maltitol are used as a fluidized bed, on which an aqueous solution of maltitol is blown to make granulation and drying. The method, however, has the problems that it has a low crystallization rate of maltitol and requires a relatively long time for the fluidized drying process, so that the apparatus is required to be enlarged and it is difficult to produce the crystalline mixture solid containing maltitol on a large scale.
When the spray-drying method was intended to be employed, it had the problems that it was difficult to adjust the crystallization rate on the preparation of the mascuite of maltitol, that the mascuite of maltitol which was sprayed into dry air caused insufficient growth of the crystal and the ratio of a glassy solid component was increased, that the powder thus produced adhered to the wall of a dryer by the influence of the insufficient growth of the crystal and could not be produced continuously, and that this method needed an expensive amount of installation cost.
On the other hand, the block grinding method is a currently employed method, which however has problems that (a) the processes are complicated and each process requires a long time, (b) containers and places for the storage of large amounts of intermediates in the middle of the crystallization are required, (c) hygienic considerations, installations and structures are required for their storage in the middle of the processes, and (d) each process of ten requires complicated operations and thus the automating or labor-saving of the process is difficult.
Therefore, a crystalline mixture solid containing maltitol in which these various problems have been solved and the conventional physical properties have been improved as well as a method for producing it are desired to be developed.